Rotor for rotary combustion engine

ABSTRACT

A partially fabricated ring gear of limited radial width is metallurgically attached to one side of the hub of a rotor for a rotary combustion engine, coaxial with the bore through the hub, and the gear teeth are then finish-machined to produce precise phasing of the rotor. A bearing bushing is then positioned in the hub bore from the opposite side of the rotor. Protrusions of the gear and the bushing on opposite sides of the rotor provide running surfaces for the axial guidance of the rotor. Rotor weight is diminished and interior accessibility improved.

United States Patent [191 Wilmers ROTOR FOR ROTARY COMBUSTION ENGINE [75] Inventor: Gottlieb Wilmers,Neckarsulm,

Germany [73] Assignees: Audi NSU Auto Union Aktiengesellschaft, Neckarsulm; Wankel G.m.b.H., Lindau. both of Germany [22] Filed: May 15, 1974 [21] Appl. No.: 470,268

Related US. Application Data [62] Division of Scr. No, 302,048, Oct. 30, 1972, Pat No.

[30] Foreign Application Priority Data Nov 16, 1971 Germany 2156814 [52] US. Cl 418/61 A [51] Int. CL" F02B 53/00 [58] Field of Search 418/61 A; 29/156 R [56] References Cited UNITED STATES PATENTS 3,059,585 11/1962 Froede ct al 418/61 A [4 1 Sept. 9, 1975 3,125,996 3/1964 Hoschele .1 123/845 3,289,647 12/1966 Turner et a1. 418/61 A 3,333,763 8/1967 Jungbluth et al. 418/61 A 3,369,740 2/1968 Abermeth 418/61 A 3,440,929 4/1969 Weissflog ct a 418/61 A 3,46l,848 8/1969 Bensinger 418/61 A 3,469,505 9/1969 Bensinger 418/61 A 3,829,944 8/1974 Wilmers 418/61 A Primary ExaminerC. J. Husar Attorney, Agenl, or Firm-Raymond P. Wallace; Victor D. Behn [5 7] ABSTRACT A partially fabricated ring gear of limited radial width is metallurgically attached to one side of the hub of a rotor for a rotary combustion engine, coaxial with the bore through the hub, and the gear teeth are then finish-machined to produce precise phasing of the rotor. A bearing bushing is then positioned in the hub bore from the opposite side of the rotor. Protrusions of the gear and the bushing on opposite sides of the rotor provide running surfaces for the axial guidance of the rotor. Rotor weight is diminished and interior accessibility improved.

2 Claims, 3 Drawing Figures ROTOR FOR ROTARY COMBUSTION ENGINE This is a division of application Ser. No. 302,048, filed Oct. 30, 1972, now US. Pat. No. 3,829,944.

BACKGROUND OF THE INVENTION This invention relates to rotors for rotary internal combustion engines of the trochoidal type, and to methods of fabricating such rotors.

Such an engine has a generally trochoidal peripheral housing and a pair of parallel end walls, a shaft transpiercing the end walls and having an eccentric portion disposed therebetween, and a multiapexed rotor of generally polygonal profile rotatably disposed on the eccentric. The rotor is hollow for internal cooling, with a peripheral wall and a pair of side walls defining its internal cavity, and has an internal hub for mounting it on the eccentric portion of the shaft; the side walls of the rotor are each provided with a circular opening.

The rotor has disposed at one side a ring gear which meshes with a pinion gear secured to one of the end walls of the engine, and the attachment of such a ring gear has caused certain difficulties in the prior art. In general it has been secured by screws to the rotor hub. This type of attachment requires a considerable radial width of the ring gear and also of the hub, so that the holes may be capable of taking the attaching screws. This large radial width of the hub adds to the rotor weight and leaves only a relatively narrow gap between the end of the rotor hub and the adjacent rotor side walls. The casting cores necessary for production of the rotor cavities must be fastened in position through this small gap, which is a time-consuming operation, and moreover the cores in this region have a very weak cross-section and break easily, increasing the cost of fabrication.

A ring gear of considerable radial width, screwed to the rotor hub as in the prior art, reduces the passage to the interior of the rotor and restricts the flow of the internal cooling fluid through the annular gap remaining between the ring gear and the adjacent side wall of the rotor.

These prior art problems of expensive casting procedures, high rotor weight, and low accessibility of the rotor interior are solved by the present invention.

SUMMARY This invention provides a rotor and a process for making it, wherein the radial width of both the rotor hub and the ring gear are relatively small, making possible the use of more stable casting cores and providing greater accessibility to the interior rotor cavity. This is accomplished by providing a rotor having a hub of small radial width, the hub having a bore therethrough of a diameter equal to or greater than the diameter of the root circle of the ring gear, and metallurgically attaching a ring gear of small radial width to one end of the hub. The ring gear may be only partially fabricated before attachment, that is, it may have no teeth or only roughly machined teeth. and attachment may be by any of various welding processes, brazing, or by soldering. After such metallurgical attachment the gear teeth are finish machined by a broaching tool or other throughpassing tool, which can readily run into the hub bore since the bore is at least as large as the root circle of the gear. After finishing the gear a bearing bushing is installed in the hub bore, which bushing may project slightly in the axial direction beyond the rotor side face to provide a running surface. The gear on the opposite side may also project beyond the rotor side face to provide a running surface on that side.

It is therefore an object of this invention to provide a lightweight rotor for a trochoidal engine.

It is another object to provide such a rotor having a hub of small radial extent to allow greater interior accessibility.

It is a further object to provide such a rotor with a metallurgically attached gear of small radial thickness.

Still another object is to provide a method of fabricating such a rotor.

Other objects and advantages will become apparent on reading the following specification in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation of the rotor of the invention, looking in the axial direction;

FIG. 2 is a cross-section on an enlarged scale, taken on line 2-2 of FIG. I; and

FIG. 3 is a fragmentary view of the area circled in FIG. 2, showing a modified embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a view of the gear side of a generally polygonal rotor according to the invention. Although the profile of the rotor is shown as generally triangular with three apex portions, it will be understood that it may have other configurations, depending on the number of lobes of the trochoidal housing of the engine in which it is to be used.

As shown in FIG. 2, the rotor has two parallel side walls 1 and 2 and a peripheral wall 3. A hub portion 4 of less axial extent than the internal space between the side walls is positioned midway therebetween, connected to the peripheral wall by ribs or apertured webs 5, the radial thickness of the hub being of minimal extent. At least one end face 6 of the hub is machined for attachment of the gear. The other end face of the hub may be machined or left as cast. A ring gear 7 is metallurgically attached to the end face 6. Such metallurgical attachment can be by means of any of various welding processes such as friction welding, electron beam welding, or laser beam welding; or the attachment can be by means of brazing or soldering. Although the rotor body may be formed of cast iron, it is preferably of lightweight metal, such as aluminum, aluminum alloy, or other alloys of lower weight than iron. The gear is preferably formed of steel.

For such means of attachment only a small radial width of the gear is necessary. The gearing in trochoidal engines of the present type does not transmit torque, but serves only for phasing to maintain the rotor in proper registry with the housing within which it turns. Since the load on the ring gear is light, great strength is not required. Hence, the radial thickness of the solid web of the gear outside the root circle of the teeth may be as little as the tooth depth, since the gear is considerably stiffened and supported by attachment to the hub. In the example shown the web thickness is about one and one-half times the tooth depth. The radial thickness of the hub at the plane of attachment need not be greater than that of the gear web.

If brazing or soldering is to be used for attachment, it is advantageous to dispose a foil or a paste of the brazing or soldering material between the gear and the hub, and fuse it in a furnace. [f it is desired to increase the welding, brazing, or soldering area, the contacting surfaces of the gear and the hub may be made conical, as shown in FIG. 3.

The gear may have fully formed teeth at the time of attachment. However, in such a case an exact phase setting of the teeth can be obtained only with complicated and expensive auxiliary equipment. Alternatively, a gear blank without teeth may be attached, and the teeth wholly fabricated after attachment. The preferable method is to attach a gear with partially formed or roughly machined teeth, and to do the finishmachining after attachment. For this reason the inner diameter 8 of the bore through the hub is at least equal to, and preferably greater than, the root circle diameter of the gear teeth 9 of the ring gear 7. Because of this difference in diameters, after attachment of the gear the teeth can be finish-machined by a broaching tool or other through-passing tool without interference with the hub.

After the teeth are machined a bearing bushing 10 is installed in the hub bore; the bushing may be pressed or shrunk into the bore, or affixed with a suitable adhesive. As is shown in FIG. 2, the gear 7 may project axially slightly beyond the face 11 of the adjacent side wall 1, and serve as a running surface for the axial guidance of the rotor against the adjacent end wall (not shown) of the housing. A corresponding guidance at the opposite side of the rotor may be obtained in that the bearing bushing 10 extends axially beyond the face 12 of the side wall 2 of the rotor.

In the inner surface of the bushing 10 are disposed two annular grooves 13 and 14, the grooves being positioned in regions approximately coplanar with the respective axial ends of the hub, preferably just within the hub. The grooves 13 and 14 delimit therebetween the bearing surface proper, and receive the lubricating oil supplied through passages in the shaft (not shown) to the bearing, after it emerges from the ends of the bearing surface. Oil dwelling in the annular grooves 13 and 14 prevents entry of air into the bearing gap occasioned by necessary clearance.

Groove 13 communicates with radial apertures 15 through bushing 10, which in turn communicate with further channels 16 which may be disposed in either the hub 4 or in the gear 7. The oil from groove 13 is thereby conducted to the interconnected hollow spaces 17 in the rotor. Channels 16 may be readily provided by cutting slots in the end face 6 of the hub prior to attachment of the gear, or they may be similar slots cut in the abutting face of the gear prior to attachment.

The annular groove 14 makes it possible for the opposite end of the bushing 10, extending axially beyond the hub, to expand freely in the radial direction without producing deformation of the actual bearing surface between the grooves 13 and 14.

If desired, instead of installing a bearing bushing, the

inner surface of the bore 8 through the hub may be coated with a layer of material having bearing properties, such as lead or a lead-containing alloy.

Side walls 1 and 2 of the rotor have therein circular openings 18 and 20 respectively, coaxial with the bore through the hub. Openings 18 and 20 have a diameter at least greater than the diameter of the bore, and preferably should be as large as possible in order to reduce rotor weight and to provide the necessary accessibility to the interior. As shown, openings 18 and 20 are as large in diameter as can be produced within the rotor periphery, and have positioned in them oil seals 19 and 21, shown schematically, which prevent the leakage of oil into the operating chambers of the engine.

By the foregoing method rotors for trochoidal engines may be made with hubs and ring gears of minimum radial extent, reducing the weight of the rotor assembly and providing greater interior accessibility. it is further possible to make the rotor of light weight metal, such as aluminum or an aluminum alloy, and the gear of steel or other metal suitable for load-bearing and capable of withstanding wear.

What is claimed is:

l. A hollow rotor for rotary engine of trochoidal type, the rotor being formed of lightweight metal and comprising a pair of parallel side walls, a peripheral wall spacing the side walls apart and integral therewith, an internal hub integrally attached to the peripheral wall and having a bore therethrough, the hub having an axial length less than the spacing between the inner surfaces of the side walls, each side wall having a circular opening therethrough providing access to the interior of the rotor, the side wall openings being of greater diameter than the outer diameter of the hub and coaxial therewith, and an intemally toothed ring gear formed of steel metallurgically attached to one axial end face of the hub and coaxial therewith, the teeth of the ring gear having a root circle diameter less than the inner diameter of the hub bore, the outer diameter of the ring gear being no greater than the outer diameter of the hub end face to allow access to the interior of the rotor, the ring gear extending axially beyond the outer face of the adjacent side wall.

2. A hollow rotor as recited in claim 1, wherein the hub bore has disposed therein a bearing bushing of greater axial length than the axial length of the hub and projecting beyond the hub at each end, the inner surface of the bushing having therein a pair of annular oilcollecting grooves each disposed approximately in the plane of the associated end face of the hub, the pair of oil-collecting grooves defining a bearing surface therebetween, the end of the bushing opposite the gear and axially outside of the bearing surface extending axially beyond the outer face of the associated side wall of the rotor, this extending end of the bushing being free to expand radially without deforming the bearing surface between the grooves. 

1. A hollow rotor for rotary engine of trochoidal type, the rotor being formed of lightweight metal and comprising a pair of parallel side walls, a peripheral wall spacing the side walls apart and integral therewith, an internal hub integrally attached to the peripheral wall and having a bore therethrough, the hub having an axial length less than the spacing between the inner surfaces of the side walls, each side wall having a circular opening therethrough providing access to the interior of the rotor, the side wall openings being of greater diameter than the outer diameter of the hub and coaxial therewith, and an internally toothed ring gear formed of steel metallurgically attached to one axial end face of the hub and coaxial therewith, the teeth of the ring gear having a root circle diameter less than the inner diameter of the hub bore, the outer diameter of the ring gear being no greater than the outer diameter of the hub end face to allow access to the interior of the rotor, the ring gear extending axially beyond the outer face of the adjacent side wall.
 2. A hollow rotor as recited in claim 1, wherein the hub bore has disposed therein a bearing bushing of greater axial length than the axial length of the hub and projecting beyond the hub at each end, the inner surface of the bushing having therein a pair of annular oil-collecting grooves each disposed approximately in the plane of the associated end face of the hub, the pair of oil-collecting grooves defining a bearing surface therebetween, the end of the bushing opposite the gear and axially outside of the bearing surface extending axially beyond the outer face of the associated side wall of the rotor, this extending end of the bushing being free to expand radially without deforming the bearing surface between the grooves. 